1. Field of the Invention
This invention relates to a semiconductor chip carrier and more particularly to a semiconductor chip carrier with a terminal and a method of fabricating a semiconductor chip carrier.
2. Prior Art
It has been the most common practice to mount a semiconductor chip on a lead frame as a carrier. However, recent technical innovation requires a substantially greater number of terminals for semiconductor chips. In order to better accommodate this requirement, an attempt has been made to use a printed wiring board as a chip carrier in lieu of a lead frame.
In the known art, the wiring boards used as a chip carrier are classified into two types based upon the characterisitcs of the substrates used therein.
The first type includes those substrates which are made primarily of resins, such as a resin plate and a laminated plate obtained by laminated-molding of prepregs which are prepared by drying after impregnating the base material with varnish of the thermosetting resin. The substrates of the first type are most widely used because they have the principal characteristics required for the substratres for wiring boards, such as having superior electric isulation. On the other hand, the high density of the contemporary semiconductor chips generates substantial heat therein and as a result, an escape for such heat has become a great concern. In addition, the noise level becomes annoying unless a magnetic shield is provided. In these regards, it has been recongnized that those first type substrates suffer from a lack of heat releasing capability and magnetic shield effect as well.
The second type includes those made of a metal plate as a core extending in the middle of the board and being referred to as a metal core board. The specific structure and performance of the metal core boards are extensively diclosed, for example, in IPC Standard 1985 by The Institute for Interconnecting and Packaging Electronic Circuits and the Hewlett-Packard Journal (August 1983). The substrates of the second type display a superior property regarding the heat releasing capability and the magnetic shield effect. However, they have an inherent disadvantage in securing electric insulation particularly between the leads and the metal core which are located very close to each other. This is particularly true with the LCC (Leadless Chip Carrier) type where terminals are located at the edge of the substrate and this structural often causes electric short circuits during soldering. Furthermore, electric short circuits may also occur at the edge of the substrate simply because of excessive moisture in the atmosphere.
In essence, those substrates of the first and the second types known in the art could not be made free from a disadvantage one way or the other; more specifically, unreliable electrical insulation or otherwise insufficient heat releasing capability and magnetic shielding effect.